CATV power supplies have used tap switching on the primary (input) winding for several years now. Such an approach allows for automatic switching of taps in the event that small changes input voltage are detected, e.g., at different locations where the power supply is deployed or during deployment due to changes to the input side conditions. Such tap switching power supplies allow for a good match between the input line voltage and the load when there is a relatively small change of input line voltage e.g., a change of 40V or less for example,
A drawback of this design is that the use of multiple taps on the input side along with the control circuitry used to determine which taps are used in the input side depending on the actual input voltage within the small range of input voltages which are supported make it difficult to implement a power supply which efficiently supports a much wider range of input voltages, e.g., a range where some of the input voltages are twice or more than the lowest support input voltage.
For this reason, tap switching power supplies used for cable TV network applications are generally limited to supporting a nominal input voltage and a limited range of voltages around the nominal input voltage with the range of voltages usually corresponding to a small fraction of the nominal input voltage. For example, a conventional tap switching input power supply with a nominal 120 Volt AC input might support a working input voltage range of 100V to 130V. Similarly a conventional tap switching power supply with a nominal 240V input may support a small range of input voltages around the 240V nominal input value.
Given the differences between 120V and 240V tap switching power supplies, service personal, who may be required to replace 120V or 240V power supplies, normally need to stock both types of supplies in their truck when going on one or more service calls where the line currents that may be encountered are not known ahead of time. This is particularly important if a service technician may be directed on a service call while on the road, since in such a case the service technician may not have time to update the inventory on the service truck prior to proceeding on the service call.
In view of the above discussion it should be appreciated that there is a need for methods and/or apparatus which would allow a single tap switching power supply to be used for both 120V and 240 input voltages and/or for a tap switching power supply which could be easily reconfigured by a service technician from a 120 V mode of operation to a 240 V mode of operation or vice versa to allow for the same power supply to be used in either a 120V or 240V application.